1. Field of the Invention
The present invention relates to a switch circuit.
2. Description of the Related Art
Each transceiver employed in mobile communications includes a switch circuit for switching an input path from and to an output path of high-frequency signals.
The switch circuit includes FETs (Field Effect Transistors) in the input and output paths, to open or close the paths, respectively. The switch circuit activates either FETs arranged in the input path or FETs arranged in the output path, and inactivates the other one FET, thereby to switch the path from one to another through which high-frequency signals flow.
In the case where a large amplitude signal is input to the above switch circuit, the FETs may undesirably be operated so as to deteriorate the waveform of their output signals.
In a switch circuit disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-46101, to prevent the deterioration in the waveform of output signals when a large amplitude signal is input to the switch circuit, an inductor and a capacitor are connected in parallel with each other between the source and drain of each FET.
However, the frequency of input signals, which can be effected by the structure including the inductor and capacitor being connected with each other, is limited by a resonance circuit including an inductor and a capacitor. In other words, if a signal has the frequency which is not in a frequency range to be limited by the resonance circuit, the waveform of output signal may be deteriorated. Hence, a problem is that the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-46101 can not be adapted for those switch circuits handling signals in a wide range of frequencies.
The entire contents of Unexamined Japanese Patent Application KOKAI Publication No. H11-46101 are incorporated herein by reference.